The present invention relates to tandem trailers and the difficulties encountered in improving the highway economy performance of these tandem trailers while maintaining sufficient maneuverability for city driving. A further aspect of the present invention relates to backing up these trailers.
Over the past few years, the use of tandem trailers has become popular and more are used on the road than ever before. The tandem arrangement permits a single truck to double its hauling capability. This is particularly important in the moving industry wherein it is desirable to move furniture in one trailer and move an automobile in the second trailer, whereas in the past the automobile either had to be driven to the destination or towed behind the first trailer.
In operation, the first trailer is connected to the tractor using a fifth wheel and kingpin arrangement commonly known in the art. Alternatively, the first vehicle may be a straight truck rather than a tractor connected to the first trailer by a dolly including a fifth wheel. The second trailer is conventionally attached to the first trailer using a dolly carrying a second fifth wheel. This arrangement does not significantly increase the cost to pull the two trailers and there is little or no loss in maneuverability so long as the tractor and trailers are traveling in a forward direction.
A problem with such tandem arrangements is that the gap between the first and second vehicle results in decreased aerodynamics which affects fuel economy at high speeds such as on highways. If the two vehicles are attached too closely, the first and second trailer will interfere with each other during turning maneuvers such as those encountered in city driving. Highways are constructed without any tight turns, allowing a much smaller turning capacity to be acceptable. However, tandem trailer assemblies must operate both on highways and in cities so a greater gap has conventionally been used to meet the minimum requirements for city operation.
An additional problem occurs when the driver of the tractor desires to back up the trailers such as when delivering or picking up a load. The trailers must be disconnected from one another and backed up separately. This is due to the arrangement of pivot points between the tandem trailers and between the front trailer and tractor. When the tractor and trailers are traveling forward there are three pivot points about which the tractor and trailers pivot, namely a pivot point between the tractor and the first trailer, a pivot point between the first trailer and the dolly, and a pivot point between the converter dolly and the second trailer. This arrangement permits the driver to make smaller radius turns, but does not permit the tractor to be backed up without disconnecting the trailers from each other. This is impractical because connecting and disconnecting the trailers every time the trailer needs to be backed up is time consuming and thus expensive to do.